We have used magnetic-field-induced birefringence as a new sensitive technique to probe the aggregation kinetics of macrocyclic molecules in solution. We have found three consecutive aggregation stages: disordered objects, ordered fibers, and a network. The transition from disordered objects to ordered fibers is found to be slow, taking days or weeks to complete. We attribute this to the molecular tails of the macrocycles, which hamper fiber formation. We anticipate that Linking aggregation kinetics to molecular properties wilt lead to a better understanding of the mechanisms by which molecules self-assemble, allowing for a more rational design of the molecular building blocks.